The amount of current flowing through an inductive load (such as a valve or solenoid, for example) can be used to control the operation of many devices. For example, the amount of current flowing through an automotive brake solenoid can determine the amount of braking pressure being applied. There are times when the current through the inductive load needs to change quickly from one current level to another current level. Referring back to the automotive brake solenoid example, there may be a need to rapidly apply a significant amount of braking pressure and then release the braking pressure. This may be needed for applications such as anti-lock braking, vehicle traction control, anti-skid control, and so forth.
One way to accomplish the rapid change in the inductive load current is to use a closed control loop to allow a voltage across the inductive load to fly-back and snub. This allows for a rapid change in the current across the inductive load.
A disadvantage of the prior art is that the rapidly changing voltage can result in a very fast current transition through the load. This change (dI/dT) may be too fast for the control loop to respond to and may result in a current undershoot in the system. In the automotive brake solenoid example, current undershoot can result in a shuttering of the brakes, which provide an unpleasant sensation (and noise) for the operator of the automobile.